1. Field of the Invention
The present invention relates to actuators and, more particularly, to a jam-tolerant rotary actuator for use in aircraft flight control systems and the like.
2. Description of the Prior Art
Actuators are widely used throughout virtually all industries to control the movement of various components. In the aerospace industry, actuators are commonly used to control the movement of wing flaps. One particular type of actuator that has been used to control such wing flap movement is a rotary actuator. One particular type of rotary actuator is the Curtiss-Wright Power Hinge.RTM. (substantially disclosed in U.S. Pat. No. 4,932,613), which has an exemplary performance record that is based on numerous applications since its initial use on the B-70 Valkyrie Wingtip Fold.
The Curtiss-Wright Power Hinge.RTM. is a rugged, compact, service-proven device combining the functions of both a hinge and an actuator. The Power Hinge features include compound epicyclic high-ratio gearing, paired support rings which replace conventional planetary carriers, self aligning planetary spindle gears, anti-friction hinge ball bearings, corrosion resistant plating, hunting tooth counts to improve life and reduce input torque fluctuations, and balanced tooth geometry to equalize bending stresses. Referring to FIG. 1, a first actuator embodiment 10 utilizing the concepts of the Curtiss-Wright Power Hinge.RTM. is shown comprising a one-stage input planetary gearset and a single slice actuator. The basic components of this first actuator embodiment 10 include a splined input drive shaft 12 with an input coupling 14 and an output coupling 16, an annular input bearing 18 with an associated input bearing retainer 20, an annular output bearing 22 with an associated output bearing retainer 24, a plurality of input planetary gears 26 with a corresponding plurality of input planetary gear shafts 28, a splined carrier 30, an input sun gear 32, a plurality of spindle gears 34, two support rings 36, a stiffener 38, a first fixed ring gear 40 with an integrated attachment lug 42, a second fixed ring gear 44 with an integrated attachment lug 46, two annular ball bearings 48, and a movable output ring gear 50 with integrated attachment lugs 52.
The design of the Power Hinge is based upon simplicity which is made possible by symmetrically balancing the tooth forces acting on each spindle gear 34. The outside gear teeth of the spindle gears 34 mesh with the teeth of the fixed ring gears 40,44 and straddle the center movable output ring gear 50. Since the tooth loads on the outside gear teeth of the spindle gears 34 are identical, no overturning moments are created on the spindle gears 34. The support rings 36 provide the only reaction required to achieve force balanced spindles. Hence, the need for a carrier assembly is eliminated.
The unique rolling spindle gear and support ring design reduces weight and package size, and permits installation of a maximum complement of spindle gears 34. Using a full complement of spindle gears 34 results in distributing load over many more gear teeth, thereby reducing the load at each tooth contact and increasing actuator capacity and life.
The two support rings 36 are used to position the spindles gears 34 radially in proper mesh with the fixed ring gears 40,44, and to react the outer mesh separating forces. The support rings 36 are positioned on either side of the center gear teeth of the spindle gears 34. Since the support rings 36 offer no circumferential restraint to the spindle gears 34, they are free to orient themselves under load to achieve optimum load sharing. The support ring outer diameter size is selected to control the fitting of the spindle gears 34 into tight mesh with the fixed ring gears 40,44, thereby controlling preload and backlash of the actuator 10.
The Power Hinge can react torque, shear, and axial thrust loads. The hinge shear and thrust loads are isolated from the hinge moment (torque) by the annular ball bearings 48 coupling the movable output ring gear 50 to the fixed ring gears 40,44. Since the fixed ring gears 40,44 are typically supported by aircraft structure, all loads originating at the output ring gear 50 are transmitted through the annular ball bearings 48 to the fixed ring gear 40,44 and to the aircraft structure. Thus, the spindle gears 34 do not experience unbalanced loads; only torque about the axis of the actuator 10.
Despite all of the important features of the Power Hinge that were just discussed, it is lacking one feature which would significantly increase its functionality. Such a feature is commonly known as jam tolerance. The definition of jam tolerance encompasses the ability of an actuator, or an actuator system, to permit continued input shaft drive capabilities in the event of a jam in the actuator, or one or more of the actuators in an actuator system, respectively, resulting from gear teeth breakage or other internal actuator failures. In the context of the aerospace industry, such a jam-tolerant feature would permit continued aircraft control flap movement in the event of a jam in one or more of the actuators in an actuator system. It is obvious why such a feature would be desirable.
Several patents have been directed toward the concept of jam-tolerant actuator designs. Of these patents, the following are of primary interest to the present invention:
In U.S. Pat. No. 4,856,379 to Jafarey, a non-jamming rotary actuator for aircraft control surfaces is disclosed wherein a cam offset extends the length of an input shaft between two side plates. The cam offset comprises an inner cam member having a first offset from the axis of the input shaft and an outer cam member having a second offset from the axis of the input shaft. Each cam member has an axially extending slot formed therein into which a shear member is press or interference fit. The interrelationship of the cam members and the shear member is such that at a maximum input torque the shear member will fail and the fixed and moving ring gears will become disengaged from the compound planetary gear by the rotation of the rotation of the inner cam member and the resulting axial movement of the outer cam member whereby the outer cam member shares the same axis as the input shaft.
In U.S. Pat. No. 5,071,397 to Grimm, a jam-tolerant geared rotary actuator is disclosed wherein ball members are disposed between a center annular ramp member which is fixed to a through shaft and two outer ramp members which are splined to the through shaft. The interrelationship of the ball members and the ramps members is such that when the through shaft experiences an excessive torque, the two outer ramp members are axially displaced against a bias of springs coupled to sun gears through planet gear radial support members integrally formed with the sun gears, thereby disconnecting a torque path within the actuator.
In U.S. Pat. No. 5,120,285 to Grimm, a jam-tolerant geared rotary actuator is disclosed comprising a compound input stage and a compound output stage doubly connected by input/output link members. The doubly connected arrangement is such that a first input is connected to a first output but also connected to a second input which is, in turn, connected to a second output so that there is an open flow path for torque and power between the input stage and the output stage. Thus, if one flow path locks up, there is always an alternative flow path so that the geared rotary actuator provides for a double flow path.
In U.S. Pat. No. 4,742,730 to Dorn et al., a failsafe rotary actuator is disclosed comprising an input shaft rotatable within an actuator housing, and first and second sun gears secured in a spaced relationship along and with the input shaft for rotation therewith. The failsafe rotary actuator further comprises planetary gears disposed for orbital rotation with and circulation about the sun gears, first and second fixed ring gears disposed for independent rotation with the planetary gears, and first and second output gears disposed for independent driving contact with the planetary gears, wherein a first load path is established between the first sun gear and the first output gear across the planetary gears in cooperative engagement with the first fixed ring gear and a second load path is established between the second sun gear and the second output gear across the planetary gears in cooperative engagement with the second fixed ring gear such that a failsafe stiff link is achieved in the event of a single mechanical failure whereby the position of a control surface connected to the output gears is maintained.
In U.S. Pat. No. 4,282,776 to Eller, overload protection for a transmission system with a planetary gear train is disclosed wherein a control member coupled to a ring gear in the planetary gear train actuates a plurality of switches so as to generate an alarm signal or initiate corrective action.
Although all of the above-discussed patents are directed toward the concept of jam tolerance in actuators and the like, none are directed toward a jam-tolerant rotary actuator incorporating shear lugs formed on an inner input sun gear member and on an inner movable output ring gear member which correspond to recesses formed in an outer input sun gear member and in an outer movable output ring gear member, respectively, where, upon application of a maximum torque to either the inner input sun gear member or the outer movable output ring gear member, the shear lugs will shear thereby allowing the inner input sun gear member to be movable independent of the outer input sun gear member or the outer movable output ring gear member to be movable independent of the inner movable output ring gear member, respectively. The present invention is directed toward such a jam-tolerant actuator.